With the "Devotion to Darkness" deck, your primary goal is to assemble many black permanents to increase your devotion to black--the number of black mana symbols (Black Mana) in the mana costs of permanents you control.

You'll want to play defensively in the early game to keep your creatures alive and counting toward your devotion. Gray Merchant of Asphodel is one of the most powerful devotion effects in the deck, so it's a good strategy to hold it until you have many other black permanents on the battlefield. Abhorrent Overlord is a powerful way to turn your devotion into a game-winning army of fliers all by itself.

Since many of your creatures are good at playing defense, you have the luxury of saving your creature-removal spells for only the biggest threats. You'll be able to gain life along the way with Gray Merchant of Asphodel, Pharika's Cure, and Insatiable Harpy. Lots of your creatures have abilities that trigger when they enter the battlefield, so cards that let you reuse them, like March of the Returned and Rescue from the Underworld, are especially potent.

Your devotion to dark magic will lead you to discover other powerful spells throughout the Theros set and beyond. Magic 2014 offers the enchantment Dark Prophecy, which adds to your devotion to black and lets you draw cards if your opponent kills your minions. Erebos, God of the Dead is an awesome addition to this deck, helping you draw more cards and shutting off your opponent's life gain. Even better, you'll often have enough devotion for him to manifest as a huge, indestructible creature!